1. Field of the Invention
The present invention relates to a lead-through type filter used in a dc line for removing noises. Particularly, the present invention relates to a lead-through type filter with a built-in rectangular element, in which instead of the conventional lead-through type capacitor, the capacitor of the lead-through type filter of the present invention is made polygonal, so that the capacitance of the capacitor can be easily managed, that the errors can be minimized, that the voltage withstanding capability is made high, and that the workability can be improved.
2. Description of the Prior Art
Generally, EMI (electro magnetic interference) noise filter can be classified based on the functions into: a low pass filter (LPF) for passing only low bands; a high pass filter (HPF) for passing only high bands; a band pass filter (BPF) for passing only a particular band; and a band rejection filter (BRF) for removing only a particular band. Further, the filters can be classified based on the constituent elements into: a passive filter composed of a combination of passive elements such as inductor, capacitor and varistor; and an active filter composed of a combination of an active element such as transistor and passive elements such as capacitor and varistor.
The general lead-through type filter which is illustrated in FIG. 1 belongs to a low pass filter if it is classified functionally, and belongs to an EMI filter if it is classified constitutionally. Such a lead-through type filter is composed of a combination of a lead-through type inductor and a lead-through type capacitor, and depending on the combinations of the elements, the filter can be formed into an a xcfx80 type, T type, or LC noise filter.
Meanwhile, the noises of various frequencies which are generated in the oscillations of the communication facilities, the broadcasting facilities and the magnetrons are released through the power supply line to be propagated into the space, and to cause noises and malfunctions in the surrounding apparatuses. The lead-through type filter is used to eliminate the noises which are released through the power supply line.
FIG. 2 is a longitudinal sectional view showing the internal constitution of the conventional lead-through type filter. Referring to FIG. 2, this conventional lead-through type filter includes a lead-through type capacitor and a lead-through type inductor, or includes only a lead-through type capacitor. That is, within a case 15 which serves as a ground terminal, a lead-through type inductor 12 made of a ferrite magnetic material and a lead-through type capacitor 13 made of a ceramic material are installed on a conductive line 11 which passes through the mentioned elements 12 and 13. Further, an epoxy resin 14 is coated on the whole device. Further, IN/OUT terminals extend to the outside of the case 15, while the case 15 is grounded to be installed on a circuit board.
As to the manufacturing process for this lead-through type filter, first the lead-through type inductor 12 and the lead-trough type capacitor 13 are manufactured. Then a conductive line 11 is made to pass through the lead-through type inductor 12 and the lead-through type capacitor 13. Then the conductive line 11 is soldered to an internal electrode 13c of the lead-trough type capacitor 13. Then the cylindrical case 15 is fitted to it, and the case 15 is soldered to an external electrode 13b of the lead-through type capacitor 13. Then the epoxy resin 14 is filled into a vacant space within the cylindrical case 15. As shown in the equivalent circuit of FIG. 4, this lead-through type filter serves as an LC low pass filter. In FIG. 5, reference code 27 indicates an electrically connected portion such as a soldered portion.
As shown in FIGS. 3a and 3b, in the lead-through type (cylindrical type) capacitor, its external circumferential surface form the external electrode 13b to be bypassingly grounded, while its internal circumferential surface form an internal electrode 13c to serve as a dc line terminal.
However, in this conventional lead-through type filter, there are roughly three problems due to the lead-through type capacitor. First, the error control becomes difficult due to the geometric contour of the lead-through type capacitor. Second, the manufacturing work becomes fastidious due to its geometric contour. Third, the thicknesses between the external and internal circumferences are not constant, and therefore, the voltage withstanding capability which is based on the thinner portion is weak. These will be described in detail below.
First the difficulty of controlling the errors will be described. In this conventional lead-through type capacitor, regardless of the step of the external circumferential surface, the external and internal circumferential surfaces are round, and there is a great difference between the areas of the two surfaces. Therefore, the capacitance management which directly affects the filtering band of the capacitor becomes difficult. Accordingly, the error control among the products becomes difficult. Therefore, if an error occurs in the form of a too large a capacitance, one end of the lead-through type capacitor is trimmed, thereby attaining to the desired capacitance value. On the other hand, if an error occurs in the form of too small a capacitance, then the product is discarded as a defective one.
Second, the manufacturing difficulty will be described. In the conventional lead-through type capacitor of the filter as shown in FIG. 3, a specially prepared die is used to manufacture the stepped external electrode of the capacitor, and therefore, the manufacturing process is difficult. Further, the diameter of the internal electrode of the capacitor has to be varied according to the diameter of the conductive line used, thereby making the manufacture difficult. Further, the electrical connection between the conductive line and the internal electrode of the capacitor has to be done by carrying out a cream-soldering into the tiny gap between the conductive line and the internal electrode of the capacitor, thereby making it difficult to manufacture the lead-through type capacitor.
Finally, the weakness of the voltage withstanding will be described, If a voltage surge occurs, an insulator breakdown can occur due to the small thickness between the external and internal electrodes of the capacitor.
The present invention is intended to overcome the above described disadvantages of the conventional technique.
Therefore it is an object of the present invention to provide a lead-through type filter with a built-in rectangular element, in which instead of the conventional lead-through type capacitor, the capacitor of the lead-through type filter is made polygonal, so that the capacitance of the capacitor can be easily managed, that the errors can be minimized, that the voltage withstanding capability is made high, and that the workability can be improved.
It is another object of the present invention to provide a lead-through type filter with a built-in rectangular element, in which the lead-through type filter having the polygonal capacitor is manufactured in an array form, so that the workability can be improved, the manufacture can be made simple, and the material used can be saved, thereby curtailing the manufacturing cost.
In achieving the above objects, the lead-through type filter having angular elements according to the present invention includes: a case to be used as an external grounding terminal; a central conductive line for supplying a dc power; at least one angular filtering element accommodated within the case and made of an angular ceramic stock, with one side electrode being attached on a face of the ceramic stock and being electrically connected to the case, and with another side electrode being attached on another face of the ceramic stock and being electrically connected to the central conductive line; and an epoxy resin layer filled into an interior of the case.
In another aspect of the present invention, the lead-trough type filter having angular elements according to the present invention includes: a multi-case having at least two element accommodating rooms and to be used as an external grounding terminal; a central conductive line for supplying a dc power; at least one angular filtering element made of an angular ceramic stock, with one side electrode being attached on a face of the ceramic stock and being electrically connected to the element accommodating rooms of the multi-case, and with another side electrode being attached on another face of the ceramic stock and being electrically connected to the central conductive line, so as to be accommodated within the element accommodating rooms of the multi-case; and an epoxy resin layer filled into an interior of the multi-case.